In the specifications and drawings of Japanese Patent Application No 2-169977, Japanese Patent Application No. 2-221364, Japanese Patent Application No. 2-221365, Japanese Patent Application No. 2-222821, and Japanese Patent Application No. 2-222823, the applicant's assignee has proposed techniques for compressing input digital audio signals and recording predetermined amounts of data as recording units in bursts.
This technology uses a magneto-optical disk as the recording medium and records and reproduces AD (adaptive differential) PCM audio data defined by the so-called CD-I (CD Interactive) or CD-ROM XA audio data format. For example, thirty-two sectors of the ADPCM data together with several additional sectors for accommodating the additional data resulting from interleave processing are used as a recording unit. The recording unit is recorded in a burst on a magneto-optical disk or on other types of recordable disk.
Several modes may be selected for ADPCM audio in a recording and reproducing apparatus using a magneto-optical disk. For example, compared with the data density of the conventional compact disc (CD), level A has a data compression ratio of two, level B has a data compression ratio of four, and level C has a data compression ratio of eight. In level B, the digital audio data is compressed by a factor of four, and the playing time of a disk recorded with level B data compression is four times that of the same capacity disk recorded in the standard CD format (CD-DA format).
Using such data compression, a considerably smaller disk can have about the same recording and playing time as a standard 12 cm CD. The smaller disc enables the equipment to be made smaller in size. Since the track velocity, i.e., the velocity of the recording track relative to the pickup head, of the smaller disk recorded using level B data compression is the same as that of a standard CD, every second, sufficient compressed data is reproduced from the disk to provide four seconds of playback time. As a result, the same compressed data can be repeatedly read out from the disk four times, by the sector, by the cluster, or by some other unit. Only one of the four readings of compressed data is actually decoded and used for the audio reproduction.
The recording signal is recorded on a spiral track on the magneto-optical disk. When the disk is reproduced, the pickup head jumps radially to return to the original track position for four successive revolutions of the disc so that the same portion of the spiral track can be read four times. The audio signal can be successfully reproduced if just one of the four repeated readings can provide compressed data with an acceptable level of integrity for the data decoding circuits. This is advantageous, since it increases the resistance of the apparatus to error playback errors due to physical disturbances. This is especially advantageous in compact portable equipment.
However, the repeated reading operation just described gives no advantage when disk being reproduces includes a recording error.
Simply repeatedly recording the same compressed data during recording provides only the same recording integrity as recording the compressed data once. Thus, effective use of the suitability of the reproduction arrangement to portable compact equipment cannot be made when using the equipment for recording.